The present invention relates to intraocular lenses for implantation into living eyes following cataract removal and, more particularly, to intraocular lenses having deformable loops.
A cross-section through the front portion of an eye, generally indicated as 30, is shown in FIG. 1. The natural lens 32 is suspended behind the iris 34 and in front of the vitreous 36 by zonules 38. Light, indicated by the dotted lines 40, passes through the cornea 42 and the pupillary opening 44 of iris 34 and thence through natural lens 32 to be focused on the retina (not shown).
Sometimes, the natural lens 32 becomes cataractous so that light 40 no longer passes therethrough in a manner sufficient to create clear images. It is common practice to remove such a cataractous lens and provide light focusing by alternate means. As shown in FIG. 2, an incision opening 46 is made in the edge of the cornea 42 adjacent iris 34, as with scalpel 48. The incision opening 46 extends over an arc as indicated by the two arrows of FIG. 2. The natural lens 32 is withdrawn through the incision opening 46 by one of two commonly employed techniques. In one, the entire natural lens 32 is severed from the zonules 38 and removed leaving the forward portion of the eye 30 appearing substantially as shown in FIG. 3. Such a lens removal is referred to as an "intracapsular extraction". In the other technique commonly employed, the anterior portion, indicated as dotted line 50 in FIG. 4, of the capsular bag, generally indicated as 52, which is the outer covering of lens 32, is removed and the contents of capsular bag 52 forming lens 32 are removed. This leaves the posterior portion 54 of capsular bag 52 intact and supported by the zonules 38. The posterior portion 54 of capsular bag 52 supported by the zonules 38 thus forms a natural barrier to the vitreous 36. Such a lens extraction is referred to as an "extracapsular extraction".
The portion within the eye in front of the iris 34 and behind cornea 42 is referred to as the "anterior chamber" and is indicated as 56. The portion behind the iris 34 and in front of the posterior portion 54 of capsular bag 52 is referred to as the "posterior chamber" and is indicated as 58.
Originally, following cataract extraction, the patient was required to wear thick glasses in order to see. The thick glasses, in addition to being heavy and unsightly, caused a magnification such that correction on only one eye was impractical. Later, in some cases, patients without a natural lens were able to use a contact lens to perform the function of the missing natural lens. Unfortunately, in the age group most prone to cataract, many patients are not able to wear or insert a contact lens.
In 1948, following World War II, a British opthamologist, Dr. Harold Ridley, was inspired to form a lens of plastic and insert it within the eye as a replacement lens. It had been found during the war that plastic material, as employed in the canopies of airplanes, which penetrated the eye was tolerated within the eye as a foreign body substance. Dr. Ridley's lens (55 in FIG. 5) was merely a disc of plastic ground to the desired optical focusing characteristics which was then placed within the posterior chamber 58 following an extracapsular extraction. The lens was intended to be held in place by entrapment between the surrounding tissues, and hopefully, by the formation of adhesions thereto. While the lens worked well in many cases, the complication rate, primarily from dislocation due to the heavy weight of the lens and the lack of positive fixation in most cases, led to much research directed at developing an intraocular lens design having a more acceptable complication rate.
To this end, in the early 1950's, emphasis shifted from the posterior chamber 58 to the anterior chamber 56, first with the Strampelli lens and later with the Choyce modifications of that basic lens design. These were rigid anterior chamber lenses such as that indicated as 60 in FIG. 6. Anterior chamber lenses according to this original design are substantially flat ribbons of plastic having a lens formed in the center thereof. Small feet 62 are formed in the ends thereof and adapted to lodge in the angle between the iris 34 and the cornea 42. Being rigid, these anterior chamber lenses cannot adapt to differences in diameter across the angle of the anterior chamber 56. Accordingly, the tip to tip dimension "d" became, and is, critical. If the length is too long, the feet 62 dig into the delicate tissue adjacent the angle containing major blood vessels of the eye. This can lead to severe problems. If the lens is too short, it can move about, and may even rub and cause damage to the highly delicate endothelium lining the inside of the cornea 42. In either case, the actual implantation must be done with extreme care as the rigid lens can cause damage to the delicate tissue of the eye if thrust into position too boldly. If the iris tissue is caught by the advancing leading edge of the lens during insertion, the iris can be sheared off.
The Choyce type anterior chamber lens according to a variation of this original concept are still very popular. Under some circumstances, a lens cannot be placed with portions in the posterior chamber. In many of these cases, and in the case of personal preference by many surgeons, anterior chamber lenses are still often used. An intraocular lens can be implanted at the time of cataract removal (primary implantation) or at a later time (secondary implantation). Anterior chamber lenses are very popular for secondary implantations. During such a secondary implantation, it is highly desirable to minimize the size of the incision made in the cornea as the longer the incision, the longer the healing process that can be expected. If the incision is small, a secondary implantation becomes almost minor surgery. Despite their continued popularity, however, anterior chamber lenses had, and still have, limitations associated with them.
In the early 1950's, the problems of rigid anterior chamber lenses were already recognized and attempts were made to correct them. For one, even when sized correctly, (i.e. the proper tip-to-tip length for the diameter of the location), a rigid anterior chamber lens, such as that indicated as 60 in FIG. 6, creates what is known as a "tender" eye. That is, as one rubs the eye or the eye tends to deform from natural movement, the rigid lens 60 creates internal localized pressure at the edge of the eye causing various sensations to the wearer. This has been described as "itching", "pain", or the feeling of "having something in the eye".
One of the earliest attempts to solve the problem of the pressures of a rigid lens and the need to have the rigid lens available in varying lengths was the Dannheim type lens. Such a lens is generally indicated as 64 in FIG. 7. The Dannheim lens 64 comprised a plastic lens body 66 having a pair of opposed, closed, nylon loops 68 extending therefrom. The intent was that the nylon loops 68, being flexible, would compress to allow the lens 64 to adapt to differing diameter eyes. Unfortunately, it is characteristic of a closed flexible loop, such as loops 68, that when longitudinal pressure is applied, as indicated by the arrow 70, the loops will bow out of the plane of the lens body 66 rather than compressing in the plane of the lens body 66 as necessary to accomplish the desired objective. Accordingly, overlength Dannheim lenses 64 typically assumed a position such as shown in FIG. 8. Thus disposed, it was highly prone to touch the delicate endothelium lining the cornea 42, with attendant complications. Moreover, the lens 64 was suspended essentially by the two points adjacent arrows 70, such that a spindle effect was created whereby the lens could rotate about its longitudinal axis creating further problems.
One of the pioneers of intraocular lens design was Dr. Joaquin Barraquer of Barcelona, Spain. Dr. Barraquer was enamoured of the concept of elastic or compressable lenses and did much work with Dannheim lenses and, later, with compressible lenses of his own design. Dr. Barraquer found that if the loops 68 of a Dannheim lens 64, as shown in FIG. 7, were cut to form two incomplete J-shaped loops 72 extending from lens body 66, a lens, generally indicated as 74 in FIG. 9, would be created which resisted the bowing upon the application of longitudinal forces and which, moreover, was highly compressible in the plane of the lens body 66.
The Barraquer lens 74 of FIG. 9 achieved the objective of being compressible so as to adapt to differing diameters of eye and, additionally, was so highly compressible so as to avoid the problems of internal pressure on tissue created by the rigid lenses. Unfortunately, the Barraquer lens 74 was unsuccessful as an anterior chamber lens for a number of reasons which can be surmised from an engineering and medical evaluation of the lens. First, the incomplete loops 72 were too compressible, such that the lens was free to move about as a result of normal movements of the patient. As with the Dannheim lens 64, the Barraquer lens 74 was suspended by two points so as to be prone to the pivoting or spindle action about the longitudinal axis. Moreover, the loops 72 were not in contact with tissue which would form adhesions which would then hold the lens in place. As a result, the total fixation was by the insufficient outward pressure of the loops 72. That is, the loops 72 were compressible to adapt to different diameters and did not create harmful forces, but, on the other hand, did not create sufficient force to hold the lens in place. Last, the loops were formed of nylon which tended to absorb moisture from the environment of the living eye and, therefore, degraded over a period of time.
Recently, the Barraquer lens design has had a revitalization as a posterior chamber lens. When implanted into the posterior chamber 58 with polypropylene substituted for nylon in the loops 72, the problems associated with that lens as an anterior chamber lens are eliminated for the most part. The Barraquer type lens 74 is implanted in the posterior chamber 58 following an extracapsular extraction. Thus, the lens body 66 is trapped between the iris 34 and the posterior 54 of capsular bag 52. The loops 72 themselves can be placed within the remnants of the capsular bag 52, outside of it, or one in and one out. Typically, adhesions will form to lens 74 and loops 72 to further fixate the lens in position.
Further refinements of the basic Barraquer lens 74 have been made available recently for use in the posterior chamber. In the Simcoe type lens, generally indicated as 76 in FIG. 10, the lens body 66 has a pair of long sweeping compressible loops 78. This lens design, developed by Dr. C. William Simcoe, is adapted to contact the area into which the lens is fixated, as indicated by the dotted circle 80, continuously at many points to eliminate the single point suspension with attendant pivoting and, simultaneously, distribute the pressure over more than one point.
The lens 82 of FIG. 12 was developed (and is indicated as presently in the process of being patented) by Dr. John Sheets. It has a pair of compound curved closed loops 84 and is specially designed to be implanted within the remnants of the capsular bag 52 following extracapsular extraction. The closed loops 84 operate in the manner of the loops 72 of the Barraquer lens 74 of FIG. 9 except that the bending is concentrated in preselected locations by the configuration of loops 84 and the resultant pressure against the edges of the remnants of the capsular bag 52 is at four points instead of two points.
Several other lens designs remain viable in the art at this time. For example, the later Ridley or Pearce lens 86 of FIG. 11 is formed of a solid piece of plastic such that there is a lens body portion 66 with three flat tab support members 88 radiating therefrom. This design of Dr. John Pearce with both two and three tab variations is presently being implanted in the posterior chamber within the capsular bag both with and without sutures for fixation.
The Copeland or Maltese Cross type lens is a solid plastic lens having four tab extensions radiating at 90.degree. intervals from the lens body. It is implanted in the pupilary opening of the iris with two opposed tabs on one side of the iris and the other two tabs on the other side.
Yet another type of lenses employing flexible loops are classified as irido-capsular lenses and are, for the most part identified with Drs. Binkhorst, Worst, and Federov. A typical example of such a lens, generally indicated as 90, is shown in FIG. 15. Whereas the lenses heretofore described have the supporting portions or loops radiating laterally outward from the edges of the lens body 66 with the supporting pressure on their extreme ends, in the irido-capsular lens 90, the loops 92 extend outward normal to the posterior surface 94 of lens body 66 from a point between the center and outer edge thereof. The loops 92 are normal to the posterior surface 94 for a distance sufficient to pass from the anterior side of iris 34 to the posterior side of iris 34 and then angle substantially parallel to the posterior side of iris 34 whereupon when placed as shown in FIG. 15, iris 34 is entrapped between the posterior surface 94 and the loops 92. The irido-capsular lenses 90 typically come with two loops (Binkhorst two-loop type) as shown in FIG. 16 or three loops (Federov type) as shown in FIG. 17. There are additional variations, not shown, on this basic theme including additional loops (Binkhorst four-loop type) or staves (Federov "Sputnik" type) radiating from the edge of the lens body 66 to provide additional support area to prevent the lens 90 from dislocating from its position within the pupilary opening 44 upon wide dilation of the iris 34.
Despite all the variations heretofore described, each is a trade-off on desirable features that one would incorporate in an intraocular lens if possible. As can be seen, previous lens designs have been suitable for location within the anterior chamber or the posterior chamber, but not both. As mentioned, it is highly desirable to minimize the size of the incision opening 46 inasmuch as the greater the length of the incision opening 46, the greater the healing process which must take place. The actual passage of the lens through the incision opening 46 during the implantation process must be accomplished in a manner such as to minimize trauma to the adjacent endothelial cells lining the cornea. The basic structure should provide a broad support resistive to rotational movement, be firm enough to maintain the lens in position, yet be resilient enough to prevent damage to the tissue in contact.
Recently, a lens has been introduced which is a different compromise to certain of the aforementioned criteria not previously addressed. This lens is shown in FIGS. 13 and 14 and is the subject of U.S. Pat. No. 4,092,743 to Dr. Charles Kelman. The Kelman lens, generally indicated as 96, is an anterior chamber lens designed to be inserted through a minimum width incision opening 46 while providing a broad support base. Its primary intent is as a replacement for the Choyce type rigid lens 60 of FIG. 6 which can be implanted through a narrow incision opening 46 but which, by contrast, has a narrow supportive area. The Kelman type lens 96 of FIGS. 13 and 14 is generally in the shape of a "7" with the lens body carried on the vertical member. For this reason, it is sometimes referred to as the "pregnant 7" lens. It is a one-piece, solid plastic lens designed to be "snaked" through the narrow incision opening. As with the lens 60 of FIG. 6, however, it is basically a rigid lens and, therefore, must be sized to the diameter. Moreover, while a degree of flexibility is claimed for the lens design (and apparently achieved, at least as compared to the Choyce type lens design according to tests conducted on the two lenses) so as to be less causing of sensitivity within the eye than the Choyce type design it is intended to replace, the virtual rigid nature of the lens still does not achieve the complete lack of sensitivity obtained by elastic loops.
Wherefore, it is the object of the present invention to provide an intraocular lens design which can be used both as an anterior chamber lens and a posterior chamber lens.
It is a further object of the present invention to provide an intraocular lens having a broad support base which can be implanted through a minimum width incision opening.
It is yet another object of the present invention to provide an intraocular lens design which is compressible in its overall tip-to-tip length sufficiently to adapt to changes in diameter of the area of placement of the order of one to two millimeters and compressible to a degree such as to virtually eliminate tenderness when placed in the anterior chamber and/or damage to contacted tissue while being sufficiently rigid to resist bowing and other movements which have heretofore rendered compressible lenses unacceptable for placement in the anterior chamber.